1. Field of the Invention
This invention relates to a direct particle agglutination immunoassay and to a kit for use therein.
2. Description of the Prior Art
Most particle agglutination immunoassays are performed using an indirect methodology. In this methodology a particle (usually polystyrene latex) is covered with an antigen. A test sample (containing free antigen) is mixed with a predetermined amount of antibody and after a short incubation time, the particulate suspension is added. If antigen is present in the test sample the antibody is consumed and is not available to bind to and crosslink (agglutinate) the antigen coated particles in the subsequent reaction. If no antigen is present in the patient sample the antibody acts to agglutinate the particulate material by bridging the antigens on adjacent particle surfaces.
The indirect particle agglutination methodology is used primarily because false negative results are not obtained for patient samples having high antigen concentrations. For various reasons, the indirect agglutination procedure is not the preferred method. One reason is that this methodology can be quite costly because each test requires both an antibody and a purified antigen. Another reason is that this methodology is tedious and time consuming in that it requires two steps, namely, the pre-incubation of the sample with the antibody and the subsequent addition of the particulate suspension.
The preferred agglutination methodology is the direct particle agglutination assay. In this method the particulate material is covered with the antibody. These antibody particles are mixed with the patient sample directly. If antigen exists in the sample, the antibody binds the antigen and the particles become aggregated. If no antigen is present, no reactio occurs. Accordingly, the direct agglutination assay requires a multi-determinant antigen and heterogenous antibody which can either be a polyclonal antibody or a mixture of monoclonal antibodies wherein each type of monoclonal antibody is specific for a different determinant site. However, the direct agglutination assay does not require purified antigen for each assay and requires only one step to perform the test. Unfortunately, the direct agglutination assay is not often used because at high antigen concentrations (as can be found with certain analytes like HCG) the particles become completely coated with antigen and the desired agglutination is thereby inhibited, thus yielding a false negative result.
Accordingly, it would be very desirable to have a direct particle agglutination assay and kit wherein the false negative result is either prevented or avoided.